Hi there,
Niche uses a Hook Element to add Stacked Image gallery.
It looks like you disabled that.
Do you want the stacked gallery on desktop? If so re-enable the Hook element.
Then add this PHP snippet to your site:
add_filter( 'generate_hooks_execute_php', '__return_true' );
https://docs.generatepress.com/article/adding-php/
OR If you want the normal carousel as its on mobile then go to Customizer > CSS and delete this:
.woocommerce-product-gallery {
display: none;
}